Electric toothbrush

ABSTRACT

The invention provides an electric toothbrush capable of changing a resonant frequency and vibration amplitude of an eccentric shaft. An electric toothbrush of the present invention includes a motor, an eccentric shaft with one end fixed to a rotation shaft of the motor, and a stem serving as a vibration transmitting component having a bearing for supporting the other end of the eccentric shaft for transmitting vibration generated in accordance with rotation of the eccentric shaft to a brush portion. In the electric toothbrush, eccentric shaft is formed so that a gravity center position is movable at least in one direction among a direction in which a distance to a shaft center is changed and an axial direction.

TECHNICAL FIELD

The present invention relates to an electric toothbrush.

BACKGROUND ART

Conventionally, there is an electric toothbrush for generating vibrationby rotating an eccentric shaft with a motor (refer to Patent Document1). In such an electric toothbrush, a gravity center position of theeccentric shaft (a distance from a gravity center to a shaft center anda position in an axial direction of the eccentric shaft) is not changed.Therefore, neither resonant frequency nor vibration amplitude ischanged.

However, there are cases where the resonant frequency and the vibrationamplitude of the eccentric shaft are appropriately changeable forvarious reasons of obtaining feel of brushing at the time of brushingteeth, a brushing effect in accordance with a part of the teeth to bebrushed, and the like.

Patent Document 1: Japanese Unexamined Patent Publication No. H10-192054

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide an electric toothbrushcapable of changing a resonant frequency and vibration amplitude of aneccentric shaft.

Means for Solving the Problems

In the present invention, the following means are adopted in order tosolve the above problems.

That is, an electric toothbrush of the present invention includes:

a motor,

an eccentric shaft with one end fixed to a rotation shaft of the motor,and

a vibration transmitting component for transmitting vibration generatedin accordance with rotation of the eccentric shaft to a brush portion,wherein

the eccentric shaft is formed so that a gravity center position ismovable at least in one direction among a direction in which a distanceto a shaft center is changed and an axial direction.

According to the present invention, when the gravity center position ofthe eccentric shaft is moved in the direction in which the distance tothe shaft center is changed, vibration amplitude of the eccentric shaftcan be changed. When the gravity center position of the eccentric shaftis moved in the axial direction, a resonant frequency of the eccentricshaft can be changed.

The eccentric shaft may include a plurality of weights positioned sothat gravity centers are shifted from the shaft center, and at least oneof the plurality of weights may be provided rotatably relative to aneccentric shaft main body.

Thereby, when the rotatable weight is rotated, a positional relationshipof the gravity centers of the weights in the rotation direction relativeto the shaft center is changed. Therefore, a distance between thegravity center position of the entire eccentric shaft and the shaftcenter can be changed.

The electric toothbrush may include a first weight fixed to theeccentric shaft main body and positioned so that a gravity center isshifted from the shaft center, and

a second weight positioned so that a gravity center is shifted from theshaft center with a rotation range regulated so that rotation relativeto the eccentric shaft main body is permitted within a fixed range,wherein

a regulated position of the second weight in a rotation direction may bedifferentiated by a rotation direction of the eccentric shaft.

Thereby, the distance between the gravity center position of theeccentric shaft and the shaft center can be changed by the rotationdirection of the eccentric shaft.

The eccentric shaft may include a weight positioned so that a gravitycenter is shifted from the shaft center, and the weight may be providedmovably in the axial direction relative to an eccentric shaft main body.

Thereby, the gravity center position of the eccentric shaft can be movedin the axial direction.

A male screw may be formed in the eccentric shaft main body, and

a female screw to be screwed onto the male screw may be formed in theweight.

Thereby, the weight can be moved in the axial direction by the rotationof the eccentric shaft main body. The moving direction of the weight canbe changed by the rotation direction of the eccentric shaft main body.

The weight may be fitted to the eccentric shaft main body slidably inthe axial direction.

Thereby, the weight is moved by gravitational force in accordance with aposture of the electric toothbrush. Thus, the gravity center position ofthe eccentric shaft can be moved in the axial direction.

The eccentric shaft may include:

a first weight fixed to the eccentric shaft main body and positioned sothat a gravity center is shifted from the shaft center, and

a second weight positioned so that a gravity center is shifted from theshaft center, the second weight being adapted to be rotatable relativeto the eccentric shaft main body, and

the first weight and the second weight may be arranged in line in theaxial direction so that a plurality of teeth provided in an end surfaceof the first weight and a plurality of teeth provided in an end surfaceof the second weight are meshed with each other, thereby forming aratchet mechanism.

Thereby, in a case where the eccentric shaft main body is rotated in acertain direction, a relative positional relationship between the firstweight and the second weight is not changed. When the eccentric shaftmain body is rotated in the opposite direction, the second weight isrotated relative to the first weight. Therefore, in this case, thedistance between the gravity center position of the eccentric shaft andthe shaft center can be changed. In a case where the second weight isrotated relative to the first weight, the second weight is also moved inthe axial direction for getting over the teeth respectively provided inthe weights. Thus, the gravity center position of the eccentric shaftcan be periodically moved in the axial direction.

The eccentric shaft may include:

an eccentric shaft main body,

a weight positioned so that a gravity center is shifted from the shaftcenter, and

a coil spring with one end fixed to the eccentric shaft main body andthe other end fixed to the weight.

Thereby, the weight is moved by the gravitational force and extensionand compression of the coil spring in accordance with the posture of theelectric toothbrush. Thus, the gravity center position of the eccentricshaft can be moved in the axial direction. The eccentric shaft main bodyand the weight are connected via the coil spring. Thus, at the time ofstart-up, the weight is rotated after the rotation of the eccentricshaft main body. Therefore, at the time of start-up, the vibrationamplitude of the eccentric shaft can be gradually increased.

The eccentric shaft may include

an eccentric shaft main body, and

a weight positioned so that a gravity center is shifted from the shaftcenter, and

the eccentric shaft main body and the weight may be arranged in line inthe axial direction while a fluid (fluid for transmitting rotation power(such as oil and grease)) is placed between the eccentric shaft mainbody and the weight.

Thereby, by the so-called principle of a fluid clutch, the weight isslowly rotated at the beginning, rotation speed is gradually increased,and the rotation speed becomes the same as rotation speed of theeccentric shaft main body in the end. Accordingly, the gravity center ofthe eccentric shaft is gradually moved from a position of the shaftcenter to a position distant from the shaft center. Therefore, at thetime of start-up, the vibration amplitude of the eccentric shaft isgradually increased.

A bearing for supporting the other end of the eccentric shaft may beprovided in the vibration transmitting component.

When such a configuration is adopted, the vibration generated in thevicinity of the bearing which is provided in the vibration transmittingcomponent can be transmitted to the brush portion. The bearing isprovided on the side of the other end of the eccentric shaft, that is,in the vicinity of the brush portion which is distant from the rotationshaft of the motor. Thus, the vibration can be efficiently transmittedto the brush portion.

The above configurations can be adopted in combination as far aspossible.

Effect of the Invention

As described above, according to the present invention, the resonantfrequency and the vibration amplitude of the eccentric shaft can bechanged.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of parts of an electrictoothbrush according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of the electric toothbrushaccording to the embodiment of the present invention.

FIGS. 3( a) and 3(b) are illustrative views for a mechanism in a casewhere a distance between a gravity center position of an eccentric shaftand a shaft center is changed in the electric toothbrush according tothe embodiment of the present invention.

FIGS. 4( a) and 4(b) are illustrative views for a mechanism in a casewhere the gravity center position of the eccentric shaft is moved in theaxial direction in the electric toothbrush according to the embodimentof the present invention.

FIG. 5 is a perspective view of the eccentric shaft of the electrictoothbrush according to a first example of the present invention.

FIG. 6 is a perspective view of the eccentric shaft of the electrictoothbrush according to the first example of the present invention,

FIG. 7 is a graph showing a relationship between a vibration frequencyand vibration amplitude in the electric toothbrush according to thefirst example of the present invention.

FIGS. 8( a) and 8(b) are perspective views of the eccentric shaft of theelectric toothbrush according to a second example of the presentinvention.

FIG. 9 is a graph showing a relationship between the vibration frequencyand the vibration amplitude in the electric toothbrush according to thesecond example of the present invention.

FIGS. 10( a) and 10(b) are perspective views of the eccentric shaft ofthe electric toothbrush according to a third example of the presentinvention.

FIGS. 11( a) and 11(b) are perspective views of the eccentric shaft ofthe electric toothbrush according to a fourth example of the presentinvention.

FIGS. 12( a) and 12(b) are perspective views of the eccentric shaft ofthe electric toothbrush according to a fifth example of the presentinvention.

FIGS. 13( a) and 13(b) are perspective views of the eccentric shaft ofthe electric toothbrush according to a sixth example of the presentinvention.

FIGS. 14( a) to 14(c) are perspective views of the eccentric shaft ofthe electric toothbrush according to a seventh example of the presentinvention.

FIG. 15 is a graph showing a relationship between elapsed time at thetime of start-up and maximum vibration amplitude in the electrictoothbrush according to the seventh example of the present invention.

FIG. 16 is an exploded view of parts of the eccentric shaft and a stemin the electric toothbrush according to the seventh example of thepresent invention.

FIG. 17 is a schematic sectional view of the eccentric shaft and thestem in the electric toothbrush according to the seventh example of thepresent invention.

FIG. 18 is an exploded view of parts of the eccentric shaft and the stemin the electric toothbrush according to the seventh example of thepresent invention.

FIG. 19 is a schematic sectional view of the eccentric shaft and thestem in the electric toothbrush according to the seventh example of thepresent invention.

DESCRIPTION OF SYMBOLS

-   1 Electric toothbrush-   2 Electric toothbrush main body-   21 Case-   22 Battery-   23 Motor-   23 a Rotation shaft-   24 Switch-   25 Operation unit-   3 Stem-   31 Bearing-   32 Inner wall surface-   4 Brush component-   41 Brush portion-   100 Eccentric shaft-   110 Eccentric shaft main body-   111, 112, 113, 114, 115, 116, 117 Eccentric shaft main body-   111 a, 112 a, 113 a, 114 a, 115 a, 116 a, 117 a Hole portion-   112 b Shaft portion-   112 c Male screw-   112 d First position regulation portion-   112 e Second position regulation portion-   113 b Insertion hole-   114 b Protruding portion-   114 c First weight-   115 b First weight-   115 c Tooth-   117X Trunk-   117Y Metal component-   117Ya Concave portion-   120 Weight-   121 First weight-   122 Second weight-   123 Weight-   124 First weight-   124 a Weight main body portion-   124 b Cutout portion-   124 c Substantially-disc portion-   125 Second weight-   125 a Weight main body portion-   125 b Shaft portion-   125 c Lock projection-   125 d Disc portion-   126 Weight-   126 a Pass-through hole-   127 Weight-   127 a Shaft portion-   127 b Shaft portion-   128 Second weight-   128 a Shaft portion-   128 b Slit portion-   129 Second weight-   129 a Shaft portion-   129 b Weight main body portion-   129 c Tooth-   130 Weight-   130 a Shaft portion-   131 Weight-   131 a Shaft portion-   131 b Convex portion

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to the drawings, the best mode for carrying out theinvention will be exemplified and described in detail based on anembodiment and examples. However, the scope of the invention is notlimited to only size, materials, shapes, and relative arrangement ofconstituent components described in the examples unless particularlyspecifically described.

Embodiment

With reference to FIGS. 1 to 4( b), an electric toothbrush according tothe embodiment of the present invention will be described. FIG. 1 is anexploded perspective view of parts of the electric toothbrush accordingto the embodiment of the present invention. FIG. 2 is a schematicsectional view of the electric toothbrush according to the embodiment ofthe present invention. FIGS. 3( a) and 3(b) are illustrative views for amechanism in a case where a distance between a gravity center positionof an eccentric shaft and a shaft center is changed in the electrictoothbrush according to the embodiment of the present invention. FIGS.4( a) and 4(b) are illustrative views for a mechanism in a case wherethe gravity center position of the eccentric shaft is moved in the axialdirection in the electric toothbrush according to the embodiment of thepresent invention.

(Electric Toothbrush)

With reference to FIGS. 1 and 2, the entire configuration and the likeof the electric toothbrush according to the embodiment of the presentinvention will be described. An electric toothbrush 1 is provided withan electric toothbrush main body 2, an eccentric shaft 100, a stem 3serving as a vibration transmitting component, and a brush component 4having a brush portion 41.

The electric toothbrush main body 2 is provided with a case 21, abattery 22 and a motor 23 accommodated inside the case 21, a switch 24for turning ON/OFF a power supply, and an operation unit 25 including agroup of buttons for changing various modes. One end of the eccentricshaft 100 is fixed to a rotation shaft 23 a of the motor 23. Theeccentric shaft 100 is formed so as to protrude from an opening of afront end of the case 21 toward the outside of the case 21. A weight 120positioned so that a gravity center is shifted from the shaft center isprovided in the eccentric shaft 100. The other end of the eccentricshaft 100 is supported by a bearing 31 provided in the stem 3.

The brush component 4 is installed so as to cover the stem 3. A mainbody part of the brush component 4 is formed by a tubular member so asto be installed to the stem 3, and the brush portion 41 is provided in afront end thereof. The brush component 4 is a consumable item and hencedetachable from the stem 3 so as to be timely replaced by a new item.

(Description of Operation of Electric Toothbrush)

An operation of the electric toothbrush 1 configured as above will bedescribed. When the power supply is turned on by the switch 24, therotation shaft 23 a of the motor 23 is rotated, and the eccentric shaft100 fixed to the rotation shaft 23 a is rotated. As described above, theweight 120 positioned so that the gravity center is shifted from theshaft center is provided in the eccentric shaft 100. Therefore, when theeccentric shaft 100 is rotated in a state that a distal end of theeccentric shaft 100 is not supported by the bearing 31, the eccentricshaft 100 itself is rotated while performing a motion as if swirlingaround the shaft center. Thereby, when the eccentric shaft 100 isrotated in a state that the eccentric shaft 100 is supported by thebearing 31, an outer wall surface of the eccentric shaft 100 in thevicinity of the distal end can be repeatedly collided with an inner wallsurface of the bearing 31 a number of times in a short period of time.

By performing such an operation, the stem 3 provided with the bearing 31can be vibrated via the bearing 31. By vibrating the stem 3, thevibration can be transmitted to the brush component 4 fixed to the stem3. Therefore, the brush portion 41 is vibrated by the vibration of thebrush component 4. Thus, when the brush portion 41 is applied ontoteeth, the teeth can be brushed.

(Eccentric Shaft)

Particularly, with reference to FIGS. 3( a), 3(b), 4(a), and 4(b), theeccentric shaft in the electric toothbrush according to the embodimentof the present invention will be described in detail. The eccentricshaft 100 in the present embodiment is formed so that a gravity centerposition is movable at least in one direction among the direction inwhich a distance to a shaft center is changed and the axial direction.

Firstly, with reference to FIGS. 3( a) and 3(b), a basic configurationand a mechanism in a case where the gravity center position of theeccentric shaft 100 is moved in the direction in which the distance tothe shaft center is changed will be described. In this case, two weights(hereinafter, referred to as the first weight 121, the second weight122) are provided in the eccentric shaft main body 110. The first weight121 and the second weight 122 are provided at positions where gravitycenters are shifted from the shaft center (in the figures, the symbol G1denotes a gravity center position of the first weight 121 and the symbolG2 denotes a gravity center position of the second weight 122). Shapesand weights of the first weight 121 and the second weight 122 are thesame.

The second weight 122 is rotatable relative to the eccentric shaft mainbody 110. FIG. 3( a) shows a case where the gravity center position 01of the first weight 121 and the gravity center position G2 of the secondweight 122 correspond to each other seen in the axial direction. In thiscase, when a weight of the eccentric shaft main body 110 is ignored, agravity center position G3 of the eccentric shaft 100 seen in the axialdirection corresponds to G1 and G2. The symbol R1 denotes a distancebetween the gravity center position G3 of the eccentric shaft 100 andthe shaft center at this time.

FIG. 3( b) shows a case where the second weight 122 is rotated by 90°from the state shown in FIG. 3( a). In this case, the gravity centerposition G1 of the first weight 121 and the gravity center position G2of the second weight 122 are in a positional relationship in which thegravity center positions are shifted from each other by 90° relative tothe shaft center seen in the axial direction. When the weight of theeccentric shaft main body 110 is ignored, the gravity center position G3of the eccentric shaft 100 seen in the axial direction is a position ofa midpoint between G1 and G2. When the symbol R2 denotes a distancebetween the gravity center position G3 of the eccentric shaft 100 andthe shaft center at this time, R2<R1.

As described above, by rotating the second weight 122, the gravitycenter position of the eccentric shaft 100 can be moved in the directionin which the distance to the shaft center is changed.

In the above description, the weight of the eccentric shaft main body110 is ignored for convenience sake. However, as a matter of course, theactual gravity center of the eccentric shaft 100 is also influenced bythe weight of the eccentric shaft main body 110. However, needless tosay, the fact remains that by rotating the second weight 122, thedistance between the gravity center of the eccentric shaft 100 and theshaft center is changed. For convenience sake of description, the casewhere the shapes and the weights of the first weight 121 and the secondweight 122 are the same is exemplified and described in order tosimplify the model. However, even when these shapes and weights aredifferentiated, needless to say, the distance between the gravity centerof the eccentric shaft 100 and the shaft center is changed. Even whenthree or more weights are provided, needless to say, by rotating atleast one of the weights, the distance between the gravity center of theeccentric shaft 100 and the shaft center is changed.

Next, with reference to FIGS. 4( a) and 4(b), a basic configuration anda mechanism in a case where the gravity center position of the eccentricshaft 100 is moved in the axial direction will be described. In thiscase, a weight 123 is provided movably in the axial direction relativeto the eccentric shaft main body 110. Thereby, a distance in the axialdirection between the bearing and a gravity center position of theweight 123 (denoted by the symbol L11 in FIG. 4( a) and the symbol L12in FIG. 4( b)) and a distance in the axial direction between a partfixed to the rotation shaft of the motor and the gravity center positionof the weight 123 (denoted by the symbol L21 in FIG. 4( a) and thesymbol L22 in FIG. 4( b)) can be changed. In FIGS. 4( a) and 4(b), FIG.4( b) shows an example in which a position of the weight 123 is movedcloser to the side of the bearing than an example shown in FIG. 4( a).At this time, L11>L12, and L21<L22.

As described above, by moving the weight 123 in the axial direction, thegravity center position of the eccentric shaft 100 can be moved in theaxial direction.

In the above description, the case of one weight is exemplified anddescribed. However, even when two or more weights are provided, needlessto say, by moving at least one of the weights in the axial direction,the gravity center position of the eccentric shaft 100 can be moved inthe axial direction.

By combining the configuration shown with reference to FIGS. 3( a) and3(b) and the configuration shown with reference to FIGS. 4( a) and 4(b),needless to say, the gravity center position of the eccentric shaft 100can be moved in the direction in which the distance to the shaft centeris changed, and at the same time, the gravity center position of theeccentric shaft 100 can be moved in the axial direction.

Advantages of the Present Embodiment

As described above, with the electric toothbrush 1 according to thepresent embodiment, the eccentric shaft 100 for vibrating the brushportion 41 is formed so that the gravity center position is movable atleast in one direction among the direction in which the distance to theshaft center is changed and the axial direction.

Therefore, by moving the gravity center position of the eccentric shaft100 in the direction in which the distance to the shaft center ischanged, the vibration amplitude of the eccentric shaft 100 can bechanged. By moving the gravity center position of the eccentric shaft100 in the axial direction, the resonant frequency of the eccentricshaft 100 can be changed.

One example of specific advantages obtained by changing the vibrationamplitude and the resonant frequency of the eccentric shaft 100 andutilization methods thereof will be described.

In a case where the teeth are brushed by using the electric toothbrush,some users may not obtain actual feel of brushing with a littlevibration of the brush portion or stimulation may be too strong for someusers with large vibration of the brush portion. Thus, by making thevibration amplitude of the eccentric shaft 100 changeable, the feel ofbrushing can be changed.

In general, in a case of the electric toothbrush for vibrating the brushportion by the eccentric shaft, the rotation number of the rotationshaft of the motor is set so that resonance is generated in variousmembers including the brush portion in order to efficiently vibrate thebrush portion. However, it is generally difficult to reliably generatethe resonance due to various errors. Thus, by making the resonantfrequency of the eccentric shaft 100 changeable, the resonance can bemore reliably generated.

It is confirmed that a vibrating manner of tips of the brush (a degreeof sideward vibration and a degree of vertical vibration) isdifferentiated by the frequency at the time of generating the resonance.When the vibrating manner of the tips of the brush is differentiated,the feel of brushing is also differentiated at the time of brushing theteeth. The vibration manner of the tip which is suitable for brushing isdifferentiated respectively for a part of the teeth to be brushed. Thus,by making the resonant frequency of the eccentric shaft 100 changeable,the vibrating manner of the tips of the brush can be changed. However,in this case, the resonance is generated with desired resonantfrequencies. Thus, there is a need for being able to set a plurality ofrotation numbers of the rotation shaft of the motor, or continuouslychange the rotation number. For example, the mode may be changed by theoperation unit 25 so as to change the rotation number to the severalother rotation numbers.

Next, several specific examples (the examples) of the eccentric shaftwill be described.

First Example

With reference to FIGS. 5 to 7, the electric toothbrush according to afirst example of the present invention will be described. The eccentricshaft according to the present example is a more specific example of theembodiment described with reference to FIGS. 3( a) and 3(b). FIGS. 5 and6 are perspective views of the eccentric shaft of the electrictoothbrush according to the first example of the present invention. FIG.7 is a graph showing a relationship between a vibration frequency andthe vibration amplitude in the electric toothbrush according to thefirst example of the present invention.

In the eccentric shaft according to the present example, a hole portion111 a into which a front end of the rotation shaft 23 a of the motor 23is fitted is provided in one end of the eccentric shaft main body 111. Afirst weight 124 is fixed to the other end of the eccentric shaft mainbody 111. In this first weight 124, a substantially-disc portion 124 cprovided with a cutout portion 124 b is provided in a distal end of aweight main body portion 124 a. A second weight 125 is provided in linein the axial direction on the side of a front end of the first weight124. In the second weight 125, a shaft portion 125 b supported by thebearing 31 of the stem 3 is provided in a front end of a weight mainbody portion 125 a. A disc portion 125 d having a lock projection 125 cis provided in the other end of the weight main body portion 125 a.

The second weight 125 and the eccentric shaft main body 111 are notfixed to each other. However, inside the electric toothbrush 1, thesecond weight 125 and the eccentric shaft main body 111 are formed sothat center shafts are not shifted from each other. In a specificconfiguration for realizing this, a convex portion (or a concaveportion) is formed on the shaft center of an end surface of the secondweight 125, a concave portion (or a convex portion) is provided on theshaft center of an end surface of the eccentric shaft main body 111 (anend surface of the first weight 124), and the second weight 125 and theeccentric shaft main body 111 are arranged in line in the axialdirection so that the convex and concave portions are fitted to eachother. Alternatively, the inner wall surface of the stem 3 may functionas a bearing for the weight main body portion 124 a of the first weight124 and the weight main body portion 125 a of the second weight 125.

With the above configuration, the second weight 125 can be rotatedwithin a range in which the lock projection 125 c is not disturbed bythe substantially-disc portion 124 c relative to the eccentric shaftmain body 111.

Therefore, in a case where the eccentric shaft main body 111 is rotatedin the arrow direction in FIG. 5, the second weight 125 is rotatedtogether with the eccentric shaft main body 111 in a state that therotation relative to the eccentric shaft main body 111 is regulated byabutting the lock projection 125 c with a left end (in the figure) ofthe cutout portion 124 b in the substantially-disc portion 124 c. Apositional relationship between the gravity center position of the firstweight 124 and the gravity center position of the second weight 125 atthis time corresponds to the model shown in FIG. 3( b).

In a case where the eccentric shaft main body 111 is rotated in thearrow direction in FIG. 6, the second weight 125 is rotated togetherwith the eccentric shaft main body 111 in a state that the rotationrelative to the eccentric shaft main body 111 is regulated by abuttingthe lock projection 125 c with a right end (in the figure) of the cutoutportion 124 b in the substantially-disc portion 124 c. A positionalrelationship between the gravity center position of the first weight 124and the gravity center position of the second weight 125 at this timecorresponds to the model shown in FIG. 3( a).

As described above, in a case where the eccentric shaft according to thepresent example is adopted, by switching the rotation direction of therotation shaft 23 a of the motor 23, the gravity center position of theeccentric shaft can be moved in the direction in which the distance tothe shaft center is changed. Thereby, the vibration amplitude of theeccentric shaft can be changed. In a case where this example is adopted,the mode may be changed by the operation unit 25 so as to switch therotation direction of the rotation shaft 23 a of the motor 23.

FIG. 7 shows the relationship between the vibration frequency and thevibration amplitude in a case where the present example is adopted. Agraph P1 in FIG. 7 corresponds to a case where the eccentric shaft isrotated in the state shown in FIG. 5, and a graph P2 corresponds to acase where the eccentric shaft is rotated in the state shown in FIG. 6.

Second Example

With reference to FIGS. 8( a), 8(b), and FIG. 9, the electric toothbrushaccording to a second example of the present invention will bedescribed. The eccentric shaft according to the present example is amore specific example of the embodiment described with reference toFIGS. 4( a) and 4(b) FIGS. 8( a) and 8(b) are perspective views of theeccentric shaft of the electric toothbrush according to the secondexample of the present invention. FIG. 9 is a graph showing arelationship between the vibration frequency and the vibration amplitudein the electric toothbrush according to the second example of thepresent invention.

In an eccentric shaft main body 112 in the eccentric shaft according tothe present example, a hole portion 112 a into which the front end ofthe rotation shaft 23 a of the motor 23 is fitted is provided in one endof the eccentric shaft main body, and a shaft portion 112 b supported bythe bearing 31 of the stem 3 is provided in the other end. A male screw112 c is formed within a predetermined range of the eccentric shaft mainbody 112 according to the present example. A first position regulationportion 112 d is provided in a lower end in an area in which the malescrew 112 c is formed, and a disc shape second position regulationportion 112 e is provided in an upper end. Pass-through holes 126 a inwhich female screws to be screwed onto the male screw 112 c are formedare provided in a weight 126 according to the present example.

With the above configuration, in a case where the eccentric shaft mainbody 112 is rotated in the arrow direction in FIG. 8( a), the weight 126is not rotated relative to the eccentric shaft main body 112 or moveddownward while being rotated by co-rotation by slower speed than theeccentric shaft main body 112. In a state that the weight 126 is movedto the first position regulation portion 112 d, the weight 126 isrotated together with the eccentric shaft main body 112. In a case wherethe eccentric shaft main body 112 is rotated in the arrow direction inFIG. 8( b), the weight 126 is not rotated relative to the eccentricshaft main body 112 or moved upward while being rotated by theco-rotation by slower speed than the eccentric shaft main body 112. In astate that the weight 126 is moved to the second position regulationportion 112 e, the weight 126 is rotated together with the eccentricshaft main body 112. FIG. 8( a) corresponds to the model of FIG. 4( a),and FIG. 8( b) corresponds to the model of FIG. 4( b). In the presentexample, sufficient clearances are desirably provided between the femalescrews formed in the pass-through holes 126 a and the male screw 112 cso that the weight 126 is more reliably moved in the axial direction ina case where the eccentric shaft main body 112 is rotated.

As described above, in a case where the eccentric shaft according to thepresent example is adopted, by switching the rotation direction of therotation shaft 23 a of the motor 23, the gravity center position of theeccentric shaft can be moved in the axial direction. Thereby, theresonant frequency of the eccentric shaft can be changed. In a casewhere this example is adopted, the mode may be changed by the operationunit 25 so as to switch the rotation direction of the rotation shaft 23a of the motor 23.

FIG. 9 shows the relationship between the vibration frequency and thevibration amplitude in a case where the present example is adopted. Agraph P3 in FIG. 9 corresponds to a case where the eccentric shaft isrotated in the state shown in FIG. 8( a), and a graph P4 corresponds toa case where the eccentric shaft is rotated in the state shown in FIG.8( b). A graph P5 in FIG. 9 corresponds to a case where the weight 126is positioned in the vicinity of a center of an area in which the malescrew 112 c is formed in the eccentric shaft main body 112.

Third Example

With reference to FIGS. 10( a) and 10(b), the electric toothbrushaccording to a third example of the present invention will be described.The eccentric shaft according to the present example is a more specificexample of the embodiment described with reference to FIGS. 4( a) and4(b). FIGS. 10( a) and 10(b) are perspective views of the eccentricshaft of the electric toothbrush according to the third example of thepresent invention.

In an eccentric shaft main body 113 in the eccentric shaft according tothe present example, a hole portion 113 a into which the front end ofthe rotation shaft 23 a of the motor 23 is fitted is provided in one endof the eccentric shaft main body, and an insertion hole 113 b isprovided in the other end. In a weight 127 in the eccentric shaftaccording to the present example, a shaft portion 127 b to be insertedinto the insertion hole 113 b is provided in one end of the weight, anda shaft portion 127 a supported by the bearing 31 of the stem 3 isprovided in the other end. In the present example, the shaft portion 127b of the weight 127 can be inserted into and taken out from theinsertion hole 113 b of the eccentric shaft main body 113 with littleinsertion and take-out force. In order to rotate the weight 127 togetherwith the eccentric shaft main body 113, sectional shapes of the shaftportion 127 b and the insertion hole 113 b which are perpendicular tothe shaft are both formed into non-circular shapes (however, a circularpart may be included partly).

With the above configuration, in a case of the eccentric shaft accordingto the present example, when the eccentric shaft is inclined so as todirect the weight 127 to face the lower side, the weight 127 is moved inthe direction in which the weight is brought distant from the eccentricshaft main body 113 by a gravitational force, and when the eccentricshaft is inclined so as to direct the weight 127 to face the upper side,the weight 127 is moved in the direction in which the weight is broughtclose to the eccentric shaft main body 113 by the gravitational force.Therefore, in a case where the eccentric shaft according to the presentexample is adopted, the gravity center position of the eccentric shaftcan be moved in the axial direction by a posture of the electrictoothbrush, and hence the resonant frequency of the eccentric shaft canbe changed. FIG. 10( a) corresponds to the model of FIG. 4( b), and FIG.10( b) corresponds to the model of FIG. 4( a).

Fourth Example

With reference to FIGS. 11( a) and 11(b), the electric toothbrushaccording to a fourth example of the present invention will bedescribed. The eccentric shaft according to the present example is amore specific example of the embodiment described with reference toFIGS. 4( a) and 4(b). FIGS. 11( a) and 11(b) are perspective views ofthe eccentric shaft of the electric toothbrush according to the fourthexample of the present invention.

In an eccentric shaft main body 114 in the eccentric shaft according tothe present example, a hole portion 114 a into which the front end ofthe rotation shaft 23 a of the motor 23 is fitted is provided in one endof the eccentric shaft main body, and a first weight 114 c provided witha protruding portion 114 b is fixed to the other end. In the presentexample, a second weight 128 is provided in line in the axial directionon the side of a distal end of the eccentric shaft main body 114. In thesecond weight 128, a slit portion 128 b into which the protrudingportion 114 b is inserted is provided in one end of the second weight,and a shaft portion 128 a supported by the bearing 31 of the stem 3 isprovided in the other end. In the present example, the protrudingportion 114 b of the eccentric shaft main body 114 can be inserted intoand taken out from the slit portion 128 b of the second weight 128 withlittle insertion and take-out force.

With the above configuration, in a case of the eccentric shaft accordingto the present example, when the eccentric shaft is inclined so as todirect the second weight 128 to face the lower side, the second weight128 is moved in the direction in which the second weight 128 is broughtdistant from the eccentric shaft main body 114 by the gravitationalforce, and when the eccentric shaft is inclined so as to direct thesecond weight 128 to face the upper side, the second weight 128 is movedin the direction in which the second weight 128 is brought close to theeccentric shaft main body 114 by the gravitational force. Therefore, ina case where the eccentric shaft according to the present example isadopted, the gravity center position of the eccentric shaft can be movedin the axial direction by the posture of the electric toothbrush, andhence the resonant frequency of the eccentric shaft can be changed. FIG.11( a) corresponds to the model of FIG. 4( b), and FIG. 11( b)corresponds to the model of FIG. 4( a).

Fifth Example

With reference to FIGS. 12( a) and 12(b), the electric toothbrushaccording to a fifth example of the present invention will be described.FIGS. 12( a) and 12(b) are perspective views of the eccentric shaft ofthe electric toothbrush according to the fifth example of the presentinvention.

In an eccentric shaft main body 115 in the eccentric shaft according tothe present example, a hole portion 115 a into which the front end ofthe rotation shaft 23 a of the motor 23 is fitted is provided in one endof the eccentric shaft main body, and a first weight 115 b is fixed tothe other end. A plurality of teeth 115 c is provided in an end surfaceof the first weight 115 b.

In the present example, a second weight 129 is provided in line in theaxial direction on the side of a distal end of the eccentric shaft mainbody 115. In the second weight 129, a shaft portion 129 a supported bythe bearing 31 of the stem 3 is provided in a distal end of a weightmain body portion 129 b. A plurality of teeth 129 c to be meshed withthe plurality of teeth 115 c provided in the first weight 115 b isprovided in the other end surface of the weight main body portion 129 b,thereby forming a ratchet mechanism.

With the above configuration, in a case of the eccentric shaft accordingto the present example, when the eccentric shaft main body 115 isrotated in the arrow direction shown in FIG. 12( a), the second weight129 is not rotated relative to the eccentric shaft main body 115 butrotated together with the eccentric shaft main body 115.

When the eccentric shaft main body 115 is rotated in the oppositedirection (the arrow direction shown in FIG. 12( b)), the second weight129 is rotated relative to the first weight 115 b fixed to the eccentricshaft main body 115. Therefore, in this case, the distance between thegravity center position of the eccentric shaft and the shaft center canbe changed. In a case where the second weight 129 is rotated relative tothe first weight 115 b, the second weight 129 is also moved in the axialdirection for getting over the teeth 115 c, 129 c respectively providedin the weights. Thus, the gravity center position of the eccentric shaftcan be periodically moved in the axial direction.

Sixth Example

With reference to FIGS. 13( a) and 13(b), the electric toothbrushaccording to a sixth example of the present invention will be described.FIGS. 13( a) and 13(b) are perspective views of the eccentric shaft ofthe electric toothbrush according to the sixth example of the presentinvention.

In an eccentric shaft main body 116 in the eccentric shaft according tothe present example, a hole portion 116 a into which the front end ofthe rotation shaft 23 a of the motor 23 is fitted is provided in one endof the eccentric shaft main body. A weight 130 is provided in line inthe axial direction on the side of a distal end of the eccentric shaftmain body 116. A shaft portion 130 a supported by the bearing 31 of thestem 3 is provided in a front end of the weight 130. In the presentexample, a coil spring 140 is provided between the eccentric shaft mainbody 116 and the weight 130. One end of the coil spring 140 is fixed tothe eccentric shaft main body 116, and the other end is fixed to theweight 130.

With the above configuration, in a case of the eccentric shaft accordingto the present example, the weight 130 is moved by the gravitationalforce and extension and compression of the coil spring 140 in accordancewith the posture of the electric toothbrush. Thus, the gravity centerposition of the eccentric shaft can be moved in the axial direction. Theeccentric shaft main body 116 and the weight 130 are connected via thecoil spring 140. Thus, at the time of start-up, the weight 130 is slowlyrotated at the beginning, rotation speed is gradually increased, and therotation speed becomes the same as rotation speed of the eccentric shaftmain body 116 at the end. FIG. 13( a) shows a state immediately afterthe start-up, and FIG. 13( b) shows a state after sufficient timeelapses and the rotation speed of the weight 130 becomes the same as therotation speed of the eccentric shaft main body 116. In the figures, thenumber of arrows indicates a difference in the rotation speed (the morethe arrows are, the faster the rotation speed is).

As described above, in a case of the present example, the gravity centerof the eccentric shaft is hardly influenced by a weight of the weight130 immediately after the start-up. As the rotation speed of the weight130 becomes faster, the influence of the weight of the weight 130gradually becomes larger. Thus, the gravity center of the eccentricshaft is gradually moved from a position of the shaft center to aposition distant from the shaft center. Therefore, at the time ofstart-up, the vibration amplitude of the eccentric shaft is graduallyincreased. Thereby, in a case of brushing the teeth, the brush portion41 can be prevented from radically vibrating immediately after the powersupply is turned on, and feel of stimulation can be suppressed.

Seventh Example

With reference to FIGS. 14( a) to 14(c) and FIG. 15, the electrictoothbrush according to a seventh example of the present invention willbe described. FIGS. 14( a) to 14(c) are perspective views of theeccentric shaft of the electric toothbrush according to the seventhexample of the present invention. FIG. 15 is a graph showing arelationship between elapsed time at the time of start-up and maximumvibration amplitude in the electric toothbrush according to the seventhexample of the present invention.

In an eccentric shaft main body 117 in the eccentric shaft according tothe present example, a hole portion 117 a into which the front end ofthe rotation shaft 23 a of the motor 23 is fitted is provided in one endof the eccentric shaft main body. A weight 131 is provided in line inthe axial direction on the side of a distal end of the eccentric shaftmain body 117. A shaft portion 131 a supported by the bearing 31 of thestem 3 is provided in a front end of the weight 131. In the presentexample, a fluid (such as oil and grease) is placed in a clearance Sbetween the eccentric shaft main body 117 and the weight 131.

With the above configuration, in a case of the eccentric shaft accordingto the present example, when the eccentric shaft main body 117 isrotated, by the so-called principle of a fluid clutch, the weight 131 isslowly rotated at the beginning, rotation speed is gradually increased,and the rotation speed becomes the same as rotation speed of theeccentric shaft main body 117 at the end. FIG. 14( a) shows a stateimmediately after the start-up, FIG. 14( b) shows a state time elapses alittle after the start-up, and FIG. 14( c) shows a state aftersufficient time elapses and the rotation speed of the weight 131 becomesthe same as the rotation speed of the eccentric shaft main body 117. Inthe figures, the number of arrows indicates a difference in the rotationspeed (the more the arrows are, the faster the rotation speed is).

As described above, in a case of the present example, the gravity centerof the eccentric shaft is hardly influenced by a weight of the weight131 immediately after the start-up. As the rotation speed of the weight131 becomes faster, the influence of the weight of the weight 131gradually becomes larger. Thus, the gravity center of the eccentricshaft is gradually moved from a position of the shaft center to aposition distant from the shaft center. Therefore, at the time ofstart-up, the vibration amplitude of the eccentric shaft is graduallyincreased. Thereby, in a case of brushing the teeth, the brush portion41 can be prevented from radically vibrating immediately after the powersupply is turned on, and the feel of stimulation can be suppressed. InFIG. 15, a graph P6 shows the elapsed time at the time of start-up andthe maximum vibration amplitude in the eccentric shaft according to thepresent example. A graph P7 in the figure shows the elapsed time at thetime of start-up and the maximum vibration amplitude in a case where theweight is fixed to the eccentric shaft (comparative example).

In the present example, the weight 131 and the eccentric shaft main body117 are not fixed to each other. However, inside the electric toothbrush1, the weight 131 and the eccentric shaft main body 117 are required tobe formed so that center shafts are not shifted from each other. Twoexamples of configurations for realizing this will be described.Configurations described below can be applied to the relationshipbetween the second weight 125 and the eccentric shaft main body 111 inthe first example described above.

<<Utilizing Convexo-Concave Fit>>

With reference to FIGS. 16 and 17, a configuration in whichconvexo-concave fit is utilized so that the center shafts of the weight131 and the eccentric shaft main body 117 are not shifted from eachother will be described. The eccentric shaft main body 117 is formed bya trunk 117X in which the hole portion 117 a is provided in one end, anda metal component 117Y excellent in a wear characteristic to be fixed toa front end of this trunk 117X. The trunk 117X is made of resin orelastomer. A concave portion 117Ya is formed in a front end of the metalcomponent 117Y. Meanwhile, a convex portion 131 b to be fitted to theconcave portion 117Ya of the metal component 117Y is provided in an endof the weight 131 on the opposite side of the shaft portion 131 a.

With the above configuration, the center shafts can be prevented frombeing shifted from each other without fixing the weight 131 and theeccentric shaft main body 117.

<<Inner Wall Surface of Stem Functioning as Bearing>>

With reference to FIGS. 18 and 19, a configuration in which an innerwall surface 32 of the stem 3 functions as a bearing so that the centershafts of the weight 131 and the eccentric shaft main body 117 are notshifted from each other will be described. The eccentric shaft main body117 is formed by the trunk 117X in which the hole portion 117 a isprovided in the one end, and the metal component 117Y excellent in thewear characteristic to be fixed to the front end of the trunk 117X. Thetrunk 117X is made of resin or elastomer. The front end of the metalcomponent 117Y is formed into a plane. The end of the weight 131 on theopposite side of the shaft portion 131 a is formed into a plane.

In this example, a clearance S between the inner wall surface 32 of thestem 3 and an outer circumferential surface of the metal component 117Yand between the inner wall surface 32 of the stem 3 and an outercircumferential surface of the weight 131 is set to be as small aspossible. Thereby, the inner wall surface 32 of the stem 3 functions asa bearing for the metal component 117Y and the weight 131.

With the above configuration, the center shafts can be prevented frombeing shifted from each other without fixing the weight 131 and theeccentric shaft main body 117.

(Others)

In the above embodiment and the examples, the case where the end of theeccentric shaft on the opposite side of the end fixed to the rotationshaft 23 a of the motor 23 is supported by the bearing 31 provided inthe stem 3 is exemplified and described. In a case where such aconfiguration is adopted, as described in the above embodiment, the stem3 is vibrated via the bearing 31, and the vibration is transmitted tothe brush component 4. Since the bearing 31 is positioned in thevicinity of the brush portion 41, the vibration can be efficientlytransmitted to the brush portion 41.

However, as the electric toothbrush in which the eccentric shaft isadopted, there is a type of electric toothbrush in which an eccentricityweight is arranged in the vicinity of the rotation shaft of the motor sothat the end of the eccentric shaft on the opposite side of the endfixed to the rotation shaft of the motor is not supported by the bearing(the distal end of the eccentric shaft serves as a free end). Thepresent invention can be also applied to such a type of electrictoothbrush. That is, the above eccentric shaft may be applied to such atype of electric toothbrush.

1. An electric toothbrush, comprising: a motor; an eccentric shaft withone end fixed to a rotation shaft of the motor; and a vibrationtransmitting component for transmitting vibration generated inaccordance with rotation of the eccentric shaft to a brush portion,wherein the eccentric shaft is formed so that a gravity center positionis movable at least in one direction among a direction in which adistance to a shaft center is changed and an axial direction.
 2. Theelectric toothbrush according to claim 1, wherein the eccentric shaftincludes a plurality of weights positioned so that gravity centers areshifted from the shaft center, and at least one of the plurality ofweights is provided rotatably relative to an eccentric shaft main body.3. The electric toothbrush according to claim 2, comprising: a firstweight fixed to the eccentric shaft main body and positioned so that agravity center is shifted from the shaft center; and a second weightpositioned so that a gravity center is shifted from the shaft centerwith a rotation range regulated so that rotation relative to theeccentric shaft main body is permitted within a fixed range, wherein aregulated position of the second weight in a rotation direction isdifferentiated by a rotation direction of the eccentric shaft.
 4. Theelectric toothbrush according to claim 1, wherein the eccentric shaftincludes a weight positioned so that a gravity center is shifted fromthe shaft center, and the weight is provided movably in the axialdirection relative to an eccentric shaft main body.
 5. The electrictoothbrush according to claim 4, wherein a male screw is formed in theeccentric shaft main body, and a female screw to be screwed onto themale screw is formed in the weight.
 6. The electric toothbrush accordingto claim 4, wherein the weight is fitted to the eccentric shaft mainbody slidably in the axial direction.
 7. The electric toothbrushaccording to claim 1, wherein the eccentric shaft includes: a firstweight fixed to an eccentric shaft main body and positioned so that agravity center is shifted from the shaft center; and a second weightpositioned so that a gravity center is shifted from the shaft center,the second weight being adapted to be rotatable relative to theeccentric shaft main body, and the first weight and the second weightare arranged in line in the axial direction so that a plurality of teethprovided in an end surface of the first weight and a plurality of teethprovided in an end surface of the second weight are meshed with eachother, thereby forming a ratchet mechanism.
 8. The electric toothbrushaccording to claim 1, wherein the eccentric shaft includes: an eccentricshaft main body; a weight positioned so that a gravity center is shiftedfrom the shaft center; and a coil spring with one end fixed to theeccentric shaft main body and the other end fixed to the weight.
 9. Theelectric toothbrush according to claim 1, wherein the eccentric shaftincludes: an eccentric shaft main body; and a weight positioned so thata gravity center is shifted from the shaft center, and the eccentricshaft main body and the weight are arranged in line in the axialdirection while a fluid is placed between the eccentric shaft main bodyand the weight.
 10. The electric toothbrush according to claim 1,wherein a bearing for supporting the other end of the eccentric shaft isprovided in the vibration transmitting component.